The examination of samples, such as by metallographic examination, requires a number of preparatory steps. For example, a sample may need to be cut or sectioned to a specific size, mounted or encapsulated in a supporting material and ground and/or polished for examination. Such samples are mounted to facilitate handling and to maintain the ability to distinguish between the sample and the material in which the sample is mounted. Mounting materials are typically resins, such as thermoset or thermoplastic resins, including phenolics, phthalates, epoxies, methacrylates and the like. Such materials are commercially available from Buehler, an ITW Company, of Lake Bluff, Ill.
Mounting can be carried out in a number of ways. One way in which to mount a sample is a compression mounting process. In a compression mounting process, the sample is placed in a chamber or mold along with the mounting compound. The sample and compound are heated under pressure for example, by use of heating coils and a hydraulic ram. After a predetermined period of time at a set temperature and pressure, the heat source is isolated from the mold, and a cooling fluid is circulated around the mold to cool the encapsulated sample. After a predetermined period of time, the pressure is released and the sample is removed from the mold.
If the encapsulated sample (i.e., the sample and the molding compound) is not sufficiently cooled prior to releasing pressure and removal from the mold, the molding compound may change shape or shrink (for example, pull away from the sample). This can result in abrasive rounding the edges of the sample during later sample preparation steps, such as grinding, which may compromise the later metallographic examination. In addition, it may be difficult to handle the encapsulated sample if it is not sufficiently cooled.
To prevent premature removal of the sample, in a typical operation, the cooling system is operated for a set period of time. This time is used regardless of whether the sample has already reached a desired final temperature. As such, and as often occurs, the cooling system is run too long and the cooling liquid, usually water from a municipal water system, is wasted.
In a compression mold system, the mold that is used, as stated above, is maintained under high pressure at a high temperature. It is not unusual for the mold to reach pressures as high as 4000 psi. within the mold or pressure chamber. In a conventional system, the sample and material are positioned in the mold and a cap is positioned on an upper end of the mold. A hydraulic ram is moved into the chamber to exert a force on the sample and material, and heating coils are actuated to heat the chamber with the material and sample. The chamber is a straight-walled cylindrical chamber and the cap includes a plug that, once the cap is locked in place, inserts into the top of the chamber. The plug fits tightly into the chamber to assure that the pressure boundary within the chamber is maintained.
One drawback to this configuration is that the plug that inserts into the top of the chamber can be difficult to insert due to the tight tolerances, and the cap may be difficult to secure or lock onto the chamber. It may also be difficult to loosen and remove the cap as the plug fits tightly in the chamber top.
In that such systems operate at high temperatures and pressures, the closure systems, that is the caps that fit onto the mold or pressure chamber are quite heavy, as they are typically fabricated from steel. In addition, the caps are mounted to the system so as to remain attached to the system. As such, the caps can be difficult to maneuver and can require considerable force (or user strength) to manipulate.
Accordingly, there is a need for a sample preparation or encapsulation system having a mold chamber that readily permits closing and locking as well as unlocking and opening the chamber cap without undue exertion by an operator. Desirably, such a system also includes cap assembly that permits readily opening and closing the system without undue force or user strength. More desirably still, such a system includes an automated cooling system that terminates water flow at a specified time, once the sample has been determined to have reached a desired final temperature.